Faster communication speeds and advances made in cloud computing in recent years have resulted in burgeoning use of near-field type wireless communication (near field communication: NFC). The NFC is typically used as electronic money mounted on smartphones and smart cards used as, for example, tickets for trains and buses, in addition to cash cards, credit cards, and other IC cards. A need exists in the NFC for enhanced security in an ID identification function that identifies an individual.
A recent trend is toward mounting the ID identification function even in, for example, memory cards that have been used only for saving personal data and making the ID identification function mounted in portable devices even more sophisticated is a major challenge.
Against this background, research and development are underway to use part-to-part variations in devices for “chip's fingerprints”. Such research is known as a physically unclonable function (PUF).
Among various types of PUFs, a static random access memory (SRAM)-PUF is being studied most. The SRAM-PUF represents a technique that uses variations in two inverters that constitute the SRAM occurring during manufacturing. A RAM-PUF[1-3] that is most popular among the various types of PUFs, in particular, is applied to the security IP and IC cards mentioned above. In addition, as a way of using the initial variations in electronic devices, applications of the PUF to a nonvolatile memory are also being studied.